Reduction of gas and water coning into oil wells



March 9, 1965 J. E. WARREN 3,172,471

REDUCTION OF GAS AND WATER CONING INTO on. WELLS Filed Nov. 21, 1960INVENTOR. JOSEPH 4-. WARREN ATTORNEY United States Patent f 3,172,471REDUCTION OF GAS AND WATER (ZONING INTO 01L WELLS Joseph E. Warren,Pittsburgh, Pa, assignor to Gulf Research & Development Company,Pittsburgh, Pa., a

corporation of Delaware Filed Nov. 21, 1960, Ser. No. 79,731 9 Claims.(Cl. 16633) This invention relates to the production of oil fromoil-bearing formations and more particularly to the reduction in therate of flow of gas and water into oil wells.

The radial flow pattern of fluids from underground formations into wellsresults in high flow velocities near the borehole of the well. Theresultant high pressure drop adjacent the well causes water presentbelow oil in the pay zone to cone upwardly around the well and flow intothe well. Similarly, gas above the oil cones downwardly and flows intothe well with the oil produced from the well.

It is common for the regulatory agencies in oil producing states topenalize operators of wells which produce at high gas to oil ratios;hence, gas coning may cause a marked reduction in the rate at which anoperator may produce oil from a well. Water coning, which increases theratio of water to oil produced in the well, is objectionable because ofthe resultant increased corrosion of equipment in the well as well asbecause of the cost of lifting, separation, and disposal of the waterproduced by the well.

Among the methods that have been used in an attempt to reduce theproduction of water and gas from oil wells is to set a plug in theborehole to a level above the oilwater interface and to set a packerbelow the gas-oil interface. Oil is then produced into the Well abovethe plug or below the packer. These methods are often largelyineffective because the coning is caused by the pressure drop from theformation into the well and increased rates of flow necessitated by thereduction in area through which the fluids flow into the well furtheraggravates the water and gas coning problem. Another method that hasbeen suggested for overcoming water and gas coning is to inject a fluidfrom the well into the water or gas zone to change the pattern ofpressure differentials surrounding a well and thereby prevent theconing. Such a method has the disadvantage of requiring separate tubingand packers as well as pumping equipment at the Well head to recycle thefluid into the water and gas zones to prevent the coning.

This invention resides in a method of reducing the flow of water and gasinto oil Wells and simultaneously stimulating production of oil from thewells in which a substantially horizontal fracture is made to extendfrom the borehole of a well into the oil zone of an oil-bearingformation. A sealing composition is then displaced into the fracture andfrom the fracture into the formation above and below the fracture andthe fracture is held open while the sealing composition sets. Thefracture is extended radially beyond the plugged walls and propped opento allow flow of oil into the outer extremities of the fracture andthrough the fracture to the well.

The single figure of the drawing is a diagrammatic illustration invertical section of a well which has been treated in accordance withthis invention to reduce the flow of gas and water into the well.

Referring to the drawing, a well indicated generally by referencenumeral 10 is drilled to a total depth 12 through an oil-bearingformation having an oil zone 14. The oilbearing formation is illustratedwith a gas cap 16 above a gas-oil interface 18. A Water layer 20 below aWater- 3,172,471 Patented Mar. 9, 1965 oil interface '22 is under theoil zone 14 of the oil-bearing formation.

Casing 24 is set in the well 10 to total depth and is cemented in placeby a sheath 26 of cement in accordance with the conventional practice.The upper end of the casing 24 is closed by a cap 28. A product tubing30 extends downwardly through the casing and through a packer 32 set inthe casing in the vicinity of the oil zone 14.

A horizontal fracture 34 is made in the oil zone 14 of the oil-bearingformation. In the cased borehole illustrated in the drawing, fracture 34is made by milling through a section of the casing and cutting ahorizontal notch through the cement sheath 26 and into the forma tionsurrounding the well 10. The horizontal notch is then extended to form afracture 34 by conventional fracturing procedures, for example, in themanner described in Patent No. 2,699,212 of Newton B. Dismukes suitablymodified to form a horizontal rather than a vertical fracture. Thecutting of the notch in the formation, which may be performed bymechanical, hydraulic, or explosive means, orients the fracturesubsequently formed in the desired plane.

The fracture 34 can be made in the formation by conventional techniquesin which a suitable liquid is pumped down through the tubing 30 at apressure high enough to overcome the overburden pressure and thestrength of the formation rock. Water or lease crude oil are com monlyused in the fracturing of formations from oil wells. In some instancesit may be desirable to add synthetic or natural gums or polymers, soaps,or gelling agents to the fracturing liquid to increase the resistance offlow of the liquid into the formation. Such viscosity-increasingmaterials can subsequently be removed or destroyed in accordance withthe usual procedures by flushing or by the introduction of a materialadapted to reduce the viscosity of the fracturing liquid.

Location of the horizontal fracture 34 in the oil zone 14 will depend onthe purpose of the fracture. If the principal problem is gas coning andfluids are to be delivered into the well only through the fracture 34,the fracture should be near the bottom of the oil zone 14. If theprincipal problem is water coning, the fracture should be located nearthe top of the oil zone 14. If it is desired to prevent both gas andwater coning the fracture is preferably located at a height hk above theoilwater interface 22 where h is the distance between the oil-waterinterface 22 and the gas-oil interface 18 and where p indicates densityand the subscripts 0, g, and w signify oil, gas, and water,respectively.

After fracture 34 has been formed, a sealing material is displaced intothe fracture. The pressure applied to the sealing material is controlledto displace the sealing material into the formation above and below thefracture rather than to extend the fracture radially.

A wide variety of sealing materials are suitable for use in thisinvention. For example, the sealing material may be merely a finelypowdered solid material such as silica powder or finely divided clayswhich damage the walls of the fracture to prevent subsequent flow offluids through those walls. A number of natural or synthetic organiccompounds which will polymerize or condense to form solid resinousmaterials, insoluble in oil and water, can be used. Typical suitablematerials are synthetic resin-forming materials such asphenolformaldehyde mixtures and urea-formaldehyde mixtures or monomersof acrylonitrile or butadiene. A large number of such natural orsynthetic materials have been suggested for displacement into formationsto seal the formations to prevent the influx of water. An aqueous slurryof hydraulic cement is suitable for use in for mations sufficientlypermeable to allow cement slurries to be displaced into them.

Another method of sealing the faces of the fracture is to displace anaqueous solution of a salt from the fracture into the formation aboveand below the fracture and follow the solution with a gaseous materialwhich penetrates the formation and reacts with the salt solution to forma precipitate for a substantial depth into the formation. An aqueoussolution of aluminum sulfate followed by gaseous ammonia, which may bemixed with an inert gas such as nitrogen or methane to preventcondensation of the ammonia, are suitable for this pur-v pose. Stillanother method which is particularly suitable when an aqueous fracturingfluid has been used is to inject silicon tetrafluoride into the fractureand displace it into the formation above and below the fracture. Silicontetrafluoride hydrolizes upon contact with water and forms a solidsiliceous deposit which effectively plugs the formation.

After injection of the sealing material into the formation a proppingagent suspended in a liquid is pumped down the Well and displaced intothe fracture. The liquid used as a medium for carrying the proppingagent into the fracture flushes the sealing composition from thefracture into the formation and thereby insures the fracture beingmaintained open. The well is then shut in for a period suflicient forthe sealing material to set to form the desired seal in the formationabove and below fracture 34 to prevent flow of fluids from the formationinto the fracture.

Following the setting of the sealing composition, a fluid, preferably aliquid, is pumped down through tubing 30 and displaced into thefracture. The pressure applied to the fluid is increased and pumping ofthe fluid into the fracture is continued at a rate to extend thefracture radially beyond the plugged walls, as indicated at 36.Preferably, a propping agent, indicated by reference numeral 38, isadded to the liquid pumped into the extension 36 after the extension hasbeen formed,'to prop the extension open.

The fracture 34 with sealed Walls adjacent the well and an unsealedextension 36 at its extremity can also be made in an essentiallycontinuous operation. The fracture 34 is formed by pumping a fracturingfluid con taining the sealing agent into the formation at pressuresadequate to fracture the formation. That fluid is followed by fracturingfluid free of the sealing composition. Pumping of the fracturing fluidfree of the sealing composition is continued for a period adequate todisplace the sealing composition into the formation and to extend thefracture radially beyond the portion of the formation containing thesealing composition. Propping agent is incorporated in the fracturingfluid free of sealing composition. After the fracture 34 has beenextended the desired distance, the well is shut in to allow the sealingcomposition to set.

Oil is produced from the Well 10 by flowing from the oil zone 14 intothe extension 36 of the fracture 34 and thence through the fracture 34into the borehole of the well. The oil is lifted from the well by anysuitable conventional means. Because of the large diameter of theextension 36, the area through which the oil can enter the extension islarge and the resultant velocity of the oil flowing into the extensionis low. As a result of the low velocity, the pressure drop from theformation into the fracture 34 is low and pressure differentialsencouraging the formation of gas and water cones are reduced to aminimum. The sealing of the walls of the I fracture adjacent the welllimits the entrance of fluids into the fracture 34 to the extension 36;hence, there is no tendency for gas and water to cone adjacent the well.

In a specific embodiment of this invention a well is drilled through anoil-bearing formation extending from a depth of 3853 feet to 3903 feet.A survey indicates a water-oil interface at 3888 feet. A notch is cut inthe formation at 3870 feet and packers are set at 3865 and 3875 feet. Alease crude oil is pumped into the formation at a rate which increasesthe pressure at the well head to 5200 pounds per square inch, at whichpressure fracturing occurs. Ten barrels of the polyisocyanatecomposition described in paragraph C, column 12 of United, States LetterPatent No. 2,889,883, is pumped into the fracture and followed by 10barrels of lease crude containing one pound per gallon of 46 mesh sand.The well is then shut in for 24 hours. Ten barrels of lease crude arepumped into the fracture and followed by 250 barrels of lease crudecontaining a thickening agent such as napalm and one pound per gallon of46 mesh sand to extend the fracture beyond the sealed walls of thefracture. The well is again shut in for 24 hours and then placed onproduction.

The process of this invention allows the formation of a single barrierwhich will prevent both gas and water coning during production of oilfrom a well. This invention is particularly useful in preventing gas orwater coning in thin pay zones because it is necessary only to make asingle fracture into the pay and there is little possibility of damagetothe barrier created to prevent coning of water or gas.

I claim:

1. A method of reducing the flow into a well of fluids other than oilduring the production of oil from an oilbearing formation penetrated bythe borehole of the Well, said oil-bearing formation having an oil zoneand a zone of a fluid other than oil adjacent to and communicating withsaid oil zone, comprising forming a substantially horizontal fracturefrom the borehole into the oil zone of the formation, injecting a fluidsealing material capable of forming a solid material insoluble in oiland in water into the fracture and into the walls of the fracture toseal said walls substantially permanently and continuously from theborehole of .the well to the outer extermities of the fracture andthereby prevent flow of oil and water through the sealed walls into thefracture, maintaining the fracture open while said walls are beingsealed, injecting a fluid into the fracture under a pressure adapted toextend the fracture radially beyond the sealed walls of the fracture,and propping the fracture and extension of the fracture whereby onproduction of the Well fluids enter the extension of the fracture andflow through the fracture to the well.

2. A method of treating a well to reduce coning into the well of fluidsother than oil in the production of oil from an oil-bearing formationpenetrated by the borehole of the well, said oil-bearing-formationhaving an oil zone and a zone of a fluid other than oil adjacent to andcommunicating with said oil zone, comprising cutting a substantiallyhorizontal notch in the oil zone, injecting a fracturing .fluid into the.notch to create a substantially horizontal fractureextending from thenotch into the oil zone of the formation, sealing the walls of thefracture with a sealing material insoluble in oil and in water whilemaintaining the fracture open to form a substantially permanent andcontinuous barrier .to flow of fluids through said walls into thefracture, extending the fraca ture radially beyond .the sealed walls ofthe fracture and propping said facture and extension of the fractureopen whereby on production of the well formation fluids enter theextension of the fracture and flow through the fracture to the well.

3. A method of treating a well to reduce coning of fluids other than oilinto the well during the production of oil from an oil-bearing formationpenetrated by the borehole of the well, said underground formationhaving an oil zone and a zone of a fluid other than oil adjacent to andcommunicating with said oil zone, comprising forming a substantiallyhorizontal fracture extending from the borehole of the well into the oilzone of the formation, injecting a fluid sealing material capable offorming a solid material insoluble in oil and in water into the fractureand into the Walls of the fracture, injecting a liquid containing apropping agent into the fracture to carry the propping agent into thefracture and displace the sealing material from the fracture into theformation adjacent the walls of the fracture, shutting the well in for aperiod to allow setting of the sealing material to form a substantiallypermanent and continuous barrier to flow through said walls into thefracture, extending the fracture radially beyond the sealed wallsthereof, and depositing a propping agent in said extension whereby onproduction of the oil fluids enter the extension of the fracture andflow through the fracture to the well.

4. A process as set forth in claim 3 in which the sealing material is aliquid capable of setting to form a synthetic resin insoluble in oil andin water 5. In a method of producing oil from a pay zone containing agas zone above an oil zone and a water zone below the oil zone, theimprovement comprising forming a substantially horizontal fractureextending from the borehole of a Well into the oil zone, displacing intothe fracture a fluid sealing composition capable of forming a solidmaterial insoluble in oil and in water, displacing a Wash liquid havinga propping agent suspended therein into the fracture to prop thefracture open and flush the sealing composition therefrom, maintainingpressure on the well to prevent flow from the formation into thefracture while the sealing composition sets to seal the walls of thefracture, extending the fracture radially beyond the sealed walls of thefracture, and depositing a propping agent in the extension of thefracture whereby fluids enter said extension and flow through thefracture for production from the well.

6. A method of treatinga well to reduce coning into the Well of fluidsother than oil during the production of oil from an oil-bearingformation penetrated by the borehole of the well, said oil-bearingformation having an oil zone and a zone of a fluid other than oiladjacent to and communicating with said oil zone, comprising forming asubstantially horizontal fracture from the borehole into the oil zone ofthe formation, injecting a propping agent into the fracture, proppingthe fracture open, injecting an aqueous solution of aluminum salt intothe fracture and from the fracture into the formation, injecting gaseousammonia into the fracture whereby said ammonia enters the formation andreacts with the aluminum salt to form a precipitate plugging theformation adjacent the walls of the fracture to form a substantiallypermanent and continuous barrier to flow of fluids through said wallsinto the fracture, extending the fracture beyond the plugged walls ofsaid fracture and depositing a propping agent in said extension of thefracture.

7. A method of treating a well to reduce coning into the well of fluidsother than oil during production of oil from an oil-bearing formationpenetrated by the borehole of the well, said oil-bearing formationhaving an oil zone and a zone of a fluid other than oil adjacent to andcommunicating with said oil zone, comprising forming a substantiallyhorizontal fracture from the borehole into the oil zone of theformation, depositing a propping agent in the fracture to prop thefracture open, injecting an aqueous fluid into the fracture and into thewalls of the fracture, displacing the aqueous fluid from the fracture,injecting silicon tetrafluoride into the walls of the fracture wherebythe silicon tetrafluoride is hydrolyzed to plug the walls of thefracture and thereby form a substantially permanent and continuousbarrier to flow of fluids through said walls into the fracture,extending the fracture radially beyond the plugged walls thereof, anddepositing a propping agent in the fracture and the extension of thefracture.

8. A method of treating an oil well penetrating an oilbearing formationhaving an oil zone and a zone of a fluid other than oil adjacent to andcommunicating with said oil zone to reduce coning of fluids other thanoil into the well comprising forming a substantially horizontal fractureextending from the well into the oil zone by injecting a fracturingfluid containing a sealing composition capable of forming a solidmaterial insoluble in oil and in water down the well and into the oilzone under a pressure adequate to fracture the formation, following thefracturing fluid containing the sealing composition with a fracturingfluid free of sealing composition to displace sealing composition fromthe fracture into the formation adjacent the walls of the fracture andto form an extension of the fracture, injecting a propping agent intothe fracture, and shutting in the Well to allow the sealing compositionto set and form a substantially permanent and continuous barrier to flowof fluid through the formation adjacent the fracture radially inwardfrom the extension.

9. A method of treating an oil well penetrating an oil-bearing formationto reduce coning of fluids other than oil into the Well duringproduction from the well, said oil-bearing formation having an oil zoneand a zone of a fluid other than oil adjacent to and communicating withsaid oil zone, comprising forming a substantially horizontal fractureextending from the Well into the oil zone, substantially permanentlyplugging the formation adjacent the walls of the fracture with amaterial insoluble in oil and in water to prevent flow of oil and ofwater from the formation through the plugged formation into thefracture, and thereafter extending the fracture radially beyond theplugged walls of the fracture to form an extension of the fracture,depositing a propping agent in the fracture and extension thereof, andreducing the pressure on the well, whereby oil flows into said extensionand through the fracture for production from the well.

References Cited in the file of this patent UNITED STATES PATENTS2,699,212 Dismukes Jan. 11, 1955 2,805,721 Maly Sept. 10, 1957 2,827,121Nowak Mar. 18, 1958 2,896,717 Howard July 28, 1959 2,959,223 Harmon eta1. Nov. 8, 1960 3,004,498 Ramos Oct. 17, 1961 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3,172,471 March 9, 1965Joseph E. Warren It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below Signed and sealed this 3rd day of August1965.

(SEAL) Attest:

- ERNEST W. SWIDER EDWARD J. BRENNER Commissioner of Patents AttostingOfficer

1. A METHOD OF REDUCING THE FLOW INTO A WELL OF FLUIDS OTHER THAN OILDURING THE PRODUCTION OF OIL FROM AN OILBEARING FORMATION PENETRATED BYTHE BOREHOLE OF THE WELL, SAID OIL-BEARING FORMATION HAVING AN OIL ZONEAND A ZONE OF A FLUID OTHER THAN OIL ADJACENT TO AND COMMUNICATING WITHSAID OIL ZONE, COMPRISING FORMING A SUBSTANTIALLY HORIZONTAL FRACTUREFROM THE BOREHOLE INTO THE OIL ZONE OF THE FORMATION, INJECTING A FLUIDSEALING MATERIAL CAPABLE OF FORMING A SOLID MATERIAL INSOLUBLE IN OILAND IN WATER INTO THE FRACTURE AND INTO THE WALLS OF THE FRACTURE TOSEAL SAID WALLS SUBSTANITALLY PERMANENTLY AND CONTINUOUSLY FROM THEBOREHOLE OF THE WELL TO THE OUTER EXTERMITIES OF THE FRACTURE ANDTHEREBY PREVENT FLOW OF OIL AND WATER THROUGH THE SEALED WALLS INTO THEFRACTURE, MAINTAINING THE FRACTURE OPEN WHILE SAID WALLS ARE BEINGSEALED, INJECTING A FLUID INTO THE FRACTURE UNDER A PRESSURE SADAPTED TOEXTEND THE FRACTURE RADIALLY BEYOND THE SEALED WALLS OF THE FRACTURE,AND PROPPING THE FRACTURE AND EXTENSION OF THE FRACTURE WHEREBY ONPRODUCTION OF THE WELL FLUIDS ENTER THE EXTENSION OF THE FRACTURE ANDFLOW THROUGH THE FRACTURE TO THE WELL.